1. Field of the Invention
The present invention relates to a light emitting device and a method of driving the same. More particularly, the present invention relates to a light emitting device for preventing a cross-talk phenomenon and a pectinated pattern and a method of driving the same.
2. Description of the Related Art
A light emitting device emits a light having a certain wavelength when certain voltage or current is provided thereto, and especially an organic electroluminescent device is self light emitting device.
FIG. 1 is a block diagram illustrating a common light emitting device.
In FIG. 1, the light emitting device includes a panel 100, a controller 102, a first scan driving circuit 104, a second scan driving circuit 106, a discharging circuit 108, a precharging circuit 110 and a data driving circuit 112. For example, the light emitting device is organic electroluminescent device.
The panel 100 includes a plurality of pixels E11 to E64 formed in cross areas of data lines D1 to D6 and scan lines S1 to S4.
The controller 102 receives display data from an outside apparatus (not shown), and controls the scan driving circuits 104 and 106, the discharging circuit 108, the precharging circuit 110 and the data driving circuit 112 by using the received display data.
The first scan driving circuit 104 transmits first scan signals to some of the scan lines S1 to S4, e.g. S1 and S3. The second scan driving circuit 106 transmits second scan signals to other scan lines S2 and S4. As a result, the scan lines S1 to S4 are connected in sequence to a ground.
The discharging circuit 108 is connected to the data lines D1 to D6 through switches SW1 to SW6. In addition, the discharging circuit 108 turns on the switches SW1 to SW6 when discharging, and so the data lines D1 to D6 are connected to a zener diode ZD. As a result, the data lines D1 to D6 is discharged up to a zener voltage of the zener diode ZD.
The precharging circuit 110 provides precharge current corresponding to the display data to the discharged data lines D1 to D6 in accordance with control of the controller 102.
The data driving circuit 112 provides data currents corresponding to the display data to the precharged data lines D1 to D6 under control of the controller 102. As a result, the pixels E11 to E64 emit light.
FIG. 2A and FIG. 2B are views illustrating schematically a light emitting device of FIG. 1. FIG. 2C and FIG. 2D are timing diagrams illustrating a process of driving the light emitting device.
Hereinafter, the process of driving the light emitting device will be described after describing cathode voltages VC11 to VC61 corresponding to a first scan line S1.
As shown in FIG. 2A, a resistor between a pixel E11 and the ground is Rs, and a resistor between a pixel E21 and the ground is Rs+Rp. In addition, a resistor between a pixel E31 and the ground is Rs+2Rp, and a resistor between a pixel E41 and the ground is Rs+3Rp. Further, a resistor between a pixel E51 and the ground is Rs+4Rp, and a resistor between a pixel E61 and the ground is Rs+5Rp.
Here, it is assumed that the data currents I11 to I61 having the same magnitude are provided to the data lines D1 to D6 so that the pixels E11 to E61 emit light having the same brightness.
In this case, the data currents I11 to I61 pass to a ground through corresponding pixels E11 to E61 and the first scan line S1. Accordingly, since the data currents I11 to I61 have the same magnitude, cathode voltages VC11 to VC61 of the pixels E11 to E61 are proportioned to resistors between corresponding pixel and the ground. Hence, the values are high in the order of the cathode voltages VC61, VC51, VC41, VC31, VC21 and VC11.
In FIG. 2B, a resistor between a pixel E12 and the ground is Rs+5Rp, and thus is higher than that between the pixel E11 and the ground. Here, it is assumed that the data current I11 passing through the first data line D1 when the first scan line S1 is connected to the ground is identical to data current I12 passing through the first data line D1 when a second scan line S2 is connected to the ground. In this case, because cathode voltages VC11 and VC12 of the pixels E11 and E12 are proportioned to corresponding resistor, the cathode voltage VC12 is higher than the cathode voltage VC11.
Hereinafter, a process of driving the light emitting device will be described in detail.
The switches SW1 to SW6 are turned on, and the scan lines S1 to S4 are connected to a non-luminescent source having the same magnitude (V2) as a driving voltage of the light emitting device, e.g. voltage corresponding to maximum brightness of data current. Accordingly, the pixels E11 to E64 does not emit light, and the data lines D1 to D6 are discharged to a zener voltage of the zener diode ZD during a first discharge period of time (dcha1).
Subsequently, the switches SW1 to SW6 are turned off.
Then, precharge current corresponding to first display data is provided to the data lines D1 to D6 during a first precharge period of time (pcha1) as shown in FIG. 2C and FIG. 2D.
Subsequently, the first scan line S1 is connected to the ground as shown in FIG. 2A, and the other scan lines S2 to S4 are connected to the non-luminescent source.
Then, the data currents I11 to I61 corresponding to the first display data are provided to the data lines D1 to D6 during a first luminescent period of time (t1) as shown in FIG. 2C and FIG. 2D. As a result, the pixels E11 to E61 emit light during the first luminescent period of time (t1).
Hereinafter, the pixel E61 is assumed to have the same brightness as the pixel E11. That is, the data currents I11 and I61 having the same magnitude are provided to the data lines D1 and D6 during the first luminescent period of time (t1).
First, the data lines D1 and D6 are discharged up to the same discharge voltage during the first discharge period of time (dcha1) when discharging as shown in FIG. 2D, and so the data lines D1 and D6 are precharged to the same precharge level, i.e. certain precharge voltage during a first precharge period of time (pcha1).
Subsequently, the data currents I11 and I61 having the same magnitude are provided to the data lines D1 and D6, respectively. In this case, since the pixels E11 and E61 are preset to emit light having the same brightness, anode voltages VA11 and VA61 of the pixels E11 and E61 rise from the precharge voltage to a voltage which is different from corresponding cathode voltages VC11 and VC61 by a certain level, and then the voltages VA11 and VA61 are saturated. This is because a pixel emits a light having brightness corresponding to difference of its anode voltage and its cathode voltage.
For example, in case that the cathode voltage VC11 of the pixel E11 and the cathode voltage VC61 of the pixel E61 are 1V and 2V, respectively, the anode voltage V61 of the pixel E61 is saturated with 7V when the anode voltage VA11 of the pixel E11 is saturated with 6V. In this case, because the data lines D1 and D6 are precharged up to the same precharge voltage, e.g. 3V, the anode voltage VA11 of the pixel E11 is saturated with 6V after rising from 3V up to 6V Whereas, the anode voltage VA61 of the pixel E61 is saturated with 7V after rising 3V up to 7V. Hence, charge amount consumed until the anode voltage VA61 of the pixel E61 is saturated is higher than that consumed until the anode voltage VA11 of the pixel E11 is saturated. Accordingly, though the pixels E11 and E61 are preset to have the same brightness, the pixel E61 emits a light having brightness smaller than the pixel E11.
Hereinafter, the process of driving the light emitting device will be described continuously.
The scan lines S1 to S4 are connected to the non-luminescent source, and the switches SW1 to SW6 are turned on. As a result, the data lines D1 to D6 is discharged up to a certain discharge voltage during a second discharge period of time (dcha2) as shown in FIG. 2C.
Subsequently, the switches SW1 to SW6 are turned off, and then precharge current corresponding to second display data is provided to the data lines D1 to D6. Here, the second display data is inputted to the controller 102 after the first display data is provided to the controller 102.
Then, the second scan line S2 is connected to the ground, and the other scan lines S1, S3 and S4 are connected to the non-luminescent source.
Subsequently, data currents I12 to I62 corresponding to the second display data are provided to the data lines D1 to D6, and so pixels E12 to E62 emit light during the second luminescent period of time (t2).
Hereinafter, the pixel E12 is preset to have the same brightness as the pixel E11.
In this case, because the resistor between the pixel E12 and the ground is higher than the resistor between the pixel E11 and the ground, the cathode voltage VC12 of the pixel E12 is higher than the cathode voltage VC11 of the pixel E11. Hence, charge amount consumed until the anode voltage VA12 of the pixel E12 is saturated is higher than that consumed until the anode voltage VA11 of the pixel E11 is saturated. Accordingly, the pixel E12 emits a light having brightness smaller than the pixel E11. This phenomenon that pixels preset to have the same brightness emit really light having different brightness is referred to as “cross-talk phenomenon”.
Hereinafter, the brightness of the pixels E11 to E61 corresponding to the first scan line S1 and the pixels E12 to E62 corresponding to the second scan line S2 will be compared.
As described above, the pixel E11 of the pixels E11 to E61 corresponding to the first scan line S1 emits a light having highest brightness of the pixels E11 to E61, and the pixel E61 emits a light having smallest brightness of the pixels E11 to E61. In addition, the pixel E12 of the pixels E12 to E62 corresponding to the second scan line S2 emits a light having smallest brightness of the pixels E12 to E62, and the pixel E62 emits a light having highest brightness of the pixels E12 to E62. Hence, brightness difference between the pixels E11 and E12 related to the first data line D1 and brightness difference between the pixels E61 and E62 related to the sixth data line D2 are higher than brightness difference between the pixels E21 to E52 related to the other data lines D2 to D5. As a result, line patterns are generated at a part between the pixels E11 and E12 and a part between the pixels E61 and E62 of the panel 100. This is referred to as “pectinated pattern”.